Summary The Piper PA-31 Navajo, serial number 31-7752151, departed Machmell, British Columbia, at about 1600 Pacific daylight time with the pilot and one passenger on board. The aircraft was climbing through 10 000 feet above sea level en route to Nanaimo when the pilot noted low and fluctuating fuel pressure readings on the number-two engine. This problem had been noted before, and company maintenance had attempted to correct it by changing the fuel flow transducer on the number-two engine. The pilot contacted his company by radio to discuss the problem and, while talking with maintenance personnel, he heard an explosion. At the same time, the passenger reported that he could see flames through the vents in the lower cowl of the number-two engine. The pilot shut the engine down according to the aircraft's emergency checklist procedure, but it took three to four minutes for the fire to stop. The pilot then diverted to Port Hardy and landed without further complications, with the airport emergency response services standing by. There were no injuries; the aircraft sustained major fire damage. Ce rapport est galement disponible en franais. Other Factual Information The PA-31 Navajo is equipped with two Lycoming TI0-540-J2BD engines. The occurrence aircraft had 10 250 airframe hours, and the number-two engine had 1 145 hours since the overhaul. Fuel is supplied to the engine by an engine-driven fuel pump (EDFP) in the accessory section of the engine. The EDFP is located about 8.5 inches forward and below the turbocharger and other hot exhaust system components. A technical inspection of the aircraft following this accident revealed extensive fire damage to the accessory section of the engine, including the engine mount and lower cowling, as well as fire damage to the right main gear door, wing lower skin, flap, and engine cargo pod. The gear door had a section of aluminum of about six inches by six inches burned away at its leading edge. The flap had a similar-size hole burnt away at its leading edge. The flame track extended from the cowl door, below the engine accessory section, to the aft-end of the nacelle cargo pod and was about 14 inches wide for its entire length. For the length of the burn track, the paint and primer had been burnt away, the skin was wrinkled, some rivet heads were missing, and two holes were burnt through the skin. The inspection also determined that the engine-driven fuel pump, part number RG 9080 J4A, had been leaking fuel at the gasket between the pump body and the relief valve cap. TSB Engineering Branch analysis showed that the leak was caused by insufficient torque on the four relief cap attaching screws. The torque on the screws was found to have ranged from 0 to 3 inch-pounds, whereas the specified screw torque is 23 to 25 inch-pounds. The manufacturer of the fuel pump, Crane-Lear Romec, had been aware of fuel pump leakage due to screw torque loss and determined that the loss of torque on these screws is a result of the gasket between the pump body and the relief valve cap taking on a set, that is, compressing but not springing back. This set problem is aggravated by thermal expansion of the pump. As the temperature of the air in the vicinity of the pump rises, the pump body and valve cap expand, further compressing the gasket. After the pump cools, the pump body and relief valve cap return to their original dimensions, whereas the gasket tends to remain in its compressed form. The torque on the four mounting screws, which secure the relief valve cap to the pump body, is applied against the gasket surface; any reduction in gasket size, under compression, will reduce the torque on the screws and the security of the valve cap. Air temperatures in the enclosed engine compartments of the PA-31 Navajo reportedly rise as high as 200 Fahrenheit (93 Celsius), especially after engine shut-down, when the cooling airflow around and through the engine is eliminated. Over time, this high-temperature operating environment precipitated the gasket set, the loss of torque on the mounting screws, and the fuel leak that contributed to the in-flight engine fire. When Lycoming became aware of this problem, they issued Service Bulletin (SB) number 406 on 19 November 1976. This SB states that the screws should be checked for torque and retorqued if necessary. Several revisions of this SB have been issued, and a new SB, number 529, was issued on 01 November 1997. SB 529 is similar to SB 406 in that it states that the screws should be checked for torque and retorqued if necessary, but SB 529 adds that compliance with the SB must be accomplished after 5 hours, but before 10 hours, of engine operation. This practice is to expose the EDFP to the heat and stress of normal operation and so cause the gasket to set. The gasket set is accompanied by a loss of screw torque. The SB requires both that the screws be then re-torqued, and that the gasket be checked for leaks every 50 hours or 6 months thereafter and replaced if leaks are found. At EDFP overhaul, the pump is not installed on an engine and, therefore, the SB cannot be complied with at that time. Following engine overhaul, the engine, with the EDFP installed, is usually operated on a test stand for 1 hour or less before the engine is returned to the operator. Since the SB requires at least 5 hours of engine operation, the SB cannot be performed at either overhaul. In Canada, Canadian Aviation Regulations (CARs) do not specify that compliance with an SB is mandatory. However, when an SB is complied with, CARs require that the performing maintenance organization enters an appropriate record in the applicable technical logbook to indicate compliance with the SB. Although CARs require a logbook record to be made to show compliance with an SB, the possibility exists of an SB being complied with, signed off, then a part being replaced with no record to indicate that the SB needs to be accomplished on the replacement part. On reviewing the records of the occurrence aircraft, investigators could find no evidence that the applicable SB had been carried out. When the pilot had used the emergency checklist procedure entitled Engine Fire in Flight in his initial response to the explosion and fire, he was directed to move the firewall fuel shut-off valve of the affected engine to the OFF position, to close the throttle, feather the propeller, and place the mixture control at IDLE CUT-OFF. The pilot was then directed by the emergency checklist to follow the Engine Securing Procedures outlined in paragraph 3.7. That check, in part, required the pilot to pull out the fuel boost pump circuit breaker. When the pilot attempted to complete this action, he found that he could not access or pull the circuit breaker for the high altitude boost pump because the location of his headset jacks interfered with the circuit breakers. He departed from the checklist procedure by first removing his headset jacks from their plugs to pull out the boost pump circuit breaker. As a result, the pilot's response to the emergency was slowed and his radio communication was degraded. The position of the headset installation in relation to the high altitude boost pump circuit breaker is reported to be common and fleet-wide for Navajo models produced after 1976, and may also involve pre-1976 models in which optional high altitude boost pump systems have been installed.